1. Field of the Invention
The present invention relates to the field of earth boring tools and more particularly to rotating bits incorporating diamond cutting elements.
2. Description of the Prior Art
Diamond bits used for reaming operations are well known to the art and are generally characterized by a plurality of paths on a bit face of the rotating bit defined by alternating channels which serve as waterways and collectors for drilling mud pumped through openings defined in the bit face for the purposes of cooling and cleaning the bit. An example of such a diamond reaming bit is shown in Rowley, "COMBINATION DRILL AND REAMER BIT", U.S. Pat. No. 3,367,430. As exemplified by Rowley, such diamond bits are characterized by a generally central opening or crowfoot through which the drilling mud is provided to a plurality of waterways which radiate from the center of the bit face and outwardly across the face to the bit gage.
Diamond bits adapted for other applications have also been devised in which the central aperture or crowfoot has been replaced by a plurality of distributed nozzles such as shown by Rohde et al, "A DIAMOND DRILLING BIT FOR SOFT AND MEDIUM HARD FORMATIONS", U.S. Pat. No. 4,098,363. In the case of Rohde, the nozzles are positioned in a spiral array so that they form a plurality of substantially longitudinal arrays in each junk slot defined in the bit face. Within each junk slot, the array is more closely positioned to the leading edge of the junk slot where the diamond cutters are positioned than to the trailing edge of the next preceding blade portion or pad disposed on the opposite side of the junk slot. The nozzles are arranged in each longitudinal array so that the nozzles in each junk slot are spaced at substantially equal distances from the leading edge of the junk slot where the cutters are positioned. By this means, the drilling fluid is uniformly distributed across the junk slots and provided for flow over the adjacent pad.
It is also well known to devise a reaming diamond bit characterized by a main body portion and a pilot portion axially extending from the main body portion. The pilot bit first opens a smaller bore which is then enlarged or reamed by the main bit body which follows as the bit rotates and drills into the rock formation. An example of such a diamond reaming bit is shown in Crake, "DIAMOND BIT", U.S. Pat. No. 2,545,195. In the Crake bit, an axial nozzle is provided in the pilot bit to supply drilling fluid to a plurality of laterally extending waterways on the pilot bit. The drilling fluid moves radially along the radially directed waterways with a portion of the drilling fluid flowing over diamond elements on the adjacent pads. The fluid is then directed along junk slots and channels provided in the gage of the pilot bit toward the main bit body. At or near the connection of the main bit body with the pilot bit, a plurality of nozzles are positioned to provide additional drilling fluid to the continuation of the pilot bit waterways and junk slots which are continued on the face of the main bit.
The cleaning and cooling action of such reamers is substantially controlled by the fluid flow pattern defined by the channels, waterways, collectors and junk slots. Thus, the highest fluid velocities are obtained in such prior art bits within the fluid courses where the flow of drilling fluid is restricted. However, the cooling and cleaning action of the drilling mud is achieved only when the drilling fluid leaves the water courses and flows over the face of the bit or pads defined between the water courses. Thus the cooling and cleaning action of such prior art diamond bits is largely determined by the distribution of fluid which can be set up by the layout of water courses and is effected only to a lesser extent by fluid dynamics or pressure distributions across the bit face.
What is needed then is design for distributing fluid across a diamond rotating bit wherein distribution of drilling fluid exploits the dynamic characteristics of drilling fluid delivered to the bit face rather than primarily relying upon passive or steady state conditions created by a particular layout of water courses and junk slots.